Dehydrogenation method

ABSTRACT

Dehydrogenatable hydrocarbons are dehydrogenated by contacting them at dehydrogenation conditions with a catalytic composite, comprising a combination of catalytically effective amounts of a platinum or palladium component, an iridium component, a rhenium component, and a tin component with a porous carrier material. A specific example of the subject dehydrogenation method involves contacting a dehydrogenatable hydrocarbon and hydrogen, at dehydrogenation conditions, with a catalytic composite comprising a combination of a platinum or palladium component, an iridium component, a rhenium component, and a tin component with a porous carrier material wherein substantially all of the platinum or palladium component, the iridium component and the rhenium component are present as the corresponding elemental metals and substantially all of the tin component is present in an oxidation state above the elemental metal, and wherein the composite contains about 0.01 to about 2 wt.% platinum or palladium, about 0.01 to about 2 wt.% iridium, about 0.01 to about 2 wt.% rhenium, and about 0.01 to about 5 wt.% tin.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a Division of my copending application Ser. No.434,476 filed Jan. 18, 1974 now U.S. Patent 3,939,220; which in turn isa Continuation-In-Part of my prior application Serial No. 304,177 filedNov. 6, 1972 and now U.S. Patent No. 3,790,473; which in turn is aContinuation-In-Part of my prior application Serial No. 142,079 filedMay 10, 1971 and now U.S. Patent No. 3,702,294; and which in turn is aContinuation-In-Part of my prior, now abandoned application Serial No.819,114 filed Apr. 24, 1969 and of my prior application Serial No.807,910 filed Mar. 17, 1969 and now U.S. Patent No. 3,740,328. All ofthe teachings of these prior applications are specifically incorporatedherein by reference.

The subject of the present invention is, broadly, an improved method fordehydrogenating a dehydrogenatable hydrocarbon to produce a hydrocarbonproduct containing the same number of carbon atoms but fewer hydrogenatoms. In another aspect, the present invention involves a method ofdehydrogenating normal paraffin hydrocarbons containing 4 to 30 carbonatoms per molecule to the corresponding normal mono-olefin with minimumproduction of side products. In yet another aspect, the present relatesto a novel multimetallic catalytic composite comprising a combination ofcatalytically effective amounts of a platinum or palladium component, aniridium component, a rhenium component, a tin component, and an alkalior alkaline earth component with a porous carrier material, whichcomposite has highly beneficial characteristics of activity, selectivityand stability when it is employed in the dehydrogenation ofdehydrogenatable hydrocarbons such as aliphatic hydrocarbons, naphthenehydrocarbons and alkylaromatic hydrocarbons.

The conception of the present information followed from my search for anovel catalytic composite possessing a hydrogenation-dehydrogenationfunction, a controllable cracking function, and superior conversion,selectivity and stability characteristics when employed in hydrocarbonconversion processes that have traditionally utilized dual-functioncatalytic composites. In my prior applications, I disclosed asignificant finding with respect to a tetrametallic catalytic compositemeeting these requirements. More specifically, I determined that acombination of iridium, rhenium and tin can be utilized, under certainconditions, to beneficially interact with the platinum or palladiumcomponent of a dual-function catalyst with a resulting markedimprovement in the performance of such a catalyst. Now I haveascertained that a catalytic composite, comprising a combination ofcatalytically effective amounts of a platinum or palladium component, aniridium component, a rhenium component and a tin component with a porouscarrier material can have superior activity, selectivity and stabilitycharacteristics when it is employed in a dehydrogenation process if theoxidation state of the metallic ingredients are carefully controlled sothat substantially all of the platinum or palladium, the iridium and therhenium components are present as the corresponding elemental metals andsubstantially all of the tin component is present in an oxidation stateabove that of the elemental metal. Moreover, I have discerned that aparticularly preferred multimetallic catalytic composite of this typecontains not only a platinum or palladium component, an iridiumcomponent, a rhenium component, and a tin component, but also an alkalior alkaline earth component.

The dehydrogenation of dehydrogenatable hydrocarbons is an importantcommercial process because of the great and expanding demand fordehydrogenated hydrocarbons for use in the manufacture of variouschemical products such as detergents, plastics, synthetic rubbers,pharmaceutical products, high octane gasoline, perfumes, drying oils,ion-exchange resins, and various other products well known to thoseskilled in the art. One example of this demand is in the manufacture ofhigh octane gasoline by using C₃ and C₄ mono-olefins to alkylateisobutane. Another example of this demand is in the area ofdehydrogenation of normal paraffin hydrocarbons to produce normalmono-olefins having 4 to 30 carbon atoms per molecule. These normalmono-olefins can, in turn, be utilized in the synthesis of a vast numberof other chemical products. For example, derivatives of normalmono-olefins have become of substantial importance to the detergentindustry where they are utilized to alkylate an aromatic, such asbenzene, with subsequent transformation of the product arylalkane into awide variety of biodegradable detergents such as the alkylaryl sulfonatetype of detergent which is most widely used today for household,industrial, and commercial purposes. Still another large class ofdetergents produced from these normal mono-olefins are the oxyalkylatedphenol derivatives in which the alkyl phenol base is prepared by thealkylation of phenol with these normal mono-olefins. Still another typeof detergents produced from these normal mono-olefins are thebiodegradable alkylsulfates formed by the direct sulfation of the normalmono-olefins. Likewise, the olefin can be subjected to directsulfonation with sodium bisulfite to make biodegradable alkylsulfonates.As a further example, these mono-olefins can be hydrated to producealcohols which then, in turn, can be used to produce plasticizers and/orsynthetic lube oils.

Regarding the use of products made by the dehydrogenation ofalkylaromatic hydrocarbons, they find wide application in industriesincluding the petroleum, petrochemical, pharmaceutical, detergent,plastic industries, and the like. For example, ethylbenzene isdehydrogenated to produce styrene which is utilized in the manufactureof polystyrene plastics, styrene-butadiene rubber, and the likeproducts. Isopropylbenzene is dehydrogenated to form alpha-methylstyrenewhich, in turn, is extensively used in polymer formation and in themanufacture of drying oils, ion exchange resins, and the like materials.

Responsive to this demand for these dehydrogenation products, the arthas developed a number of alternative methods to produce them incommercial quantities. One method that is widely utilized involves theselective dehydrogenation of a dehydrogenatable hydrocarbon bycontacting the hydrocarbon with a suitable catalyst at dehydrogenationconditions. As is the case with most catalytic procedures, the principalmeasure of effectiveness for this dehydrogenation method involves theability to perform its intended function with minimum interference ofside reactions for extended periods of time. The analytical terms usedin the art to broadly measure how well a particular catalyst performsits intended functions in a particular hydrocarbon conversion reactionare activity, selectivity and stability, and for purposes of discussionhere these terms are generally defined for a given reactant as follows:(1) activity is a measure of the catalyst's ability to convert thehydrocarbon reactant into products at a specified severity level whereseverity level means the specific reaction conditions used -- that is,the temperature, pressure, contact time, and presence of diluents suchas H₂ ; (2) selectivity usually refers to the amount of desired productor products obtained relative to the amount of the reactant charged orconverted; (3) stability refers to the rate of change with time of theactivity and selectivity parameters--obviously the smaller rate implyingthe more stable catalyst. More specifically, in a dehydrogenationprocess, activity commonly refers to the amount of conversion that takesplace for a given dehydrogenatable hydrocarbon at a specified severitylevel and is typically measured on the basis of disappearance of thedehydrogenatable hydrocarbon; selectivity is typically measured by theamount, calculated on a mole percent of converted dehydrogenatablehydrocarbon basis, of the desired dehydrogenated hydrocarbon obtained atthe particular severity level; and stability is typically equated to therate of change with time of activity as measured by disappearance of thedehydrogenatable hydrocarbon and of selectivity as measured by theamount of desired hydrocarbon produced. Accordingly, the major problemfacing workers in the hydrocarbon dehydrogenation art is the developmentof a more active and selective catalytic composite that has goodstability characteristics.

I have now found a catalytic composite which possesses improvedactivity, selectivity, and stability when it is employed in a processfor the dehydrogenation of dehydrogenatable hydrocarbons. In particular,I have determined that a combination of catalytically effective amountsof a platinum or palladium component, an iridium component, a rheniumcomponent and a tin component with a porous, refractory carrier materialcan enable the performance of a dehydrogenation process to besubstantially improved. Moreover, particularly good results are obtainedwhen this composite is combined with an alkali or alkaline earthcomponent and utilized to produce dehydrogenated hydrocarbons containingthe same carbon structure as the reactant hydrocarbon but fewer hydrogenatoms. This last composite is particularly useful in the dehydrogenationof long chain normal paraffins to produce the corresponding normalmono-olefin with minimization of side reactions such as skeletalisomerization, aromatization, and cracking.

It is, accordingly, one object of the present invention to provide anovel method for the dehydrogenation of dehydrogenatable hydrocarbonsutilizing a multimetallic catalytic composite comprising a platinum orpalladium component, an iridium component, a rhenium component and a tincomponent combined with a porous carrier material. A second object is toprovide a novel nonacidic catalytic composite having superiorperformance characteristics when utilized in a dehydrogenation process.Another object is to provide an improved method for the dehydrogenationof normal paraffin hydrocarbons to produce normal mono-olefins whichmethod minimizes undesirable side reactions such as cracking, skeletalisomerization and aromatization.

In brief summary, one embodiment of the present invention involves amethod for dehydrogenating a dehydrogenatable hydrocarbon whichcomprises contacting the hydrocarbon with a multimetallic catalyticcomposite, containing a platinum or palladium component, an iridiumcomponent, a rhenium component and a tin component combined with aporous carrier material, at dehydrogenation conditions. Moreover,substantially all of the platinum or palladium, iridium and rhenium arepresent in the composite as the corresponding elemental metals andsubstantially all of the tin component is present in an oxidation stateabove that of the elemental metal. Further, these components are presentin this composite in amounts, calculated on an elemental basis,sufficient to result in the composite containing about 0.01 to about 2wt. % platinum or palladium, about 0.01 to about 2 wt. % iridium, about0.01 to about 2 wt. % rhenium and about 0.01 to about 5 wt. % tin.

A second embodiment relates to the dehydrogenation method described inthe first embodiment wherein the dehydrogenatable hydrocarbon is analiphatic compound containing 2 to 30 carbon atoms per molecule.

A third embodiment comprehends a catalytic composite comprising acombination of a platinum or palladium component, an iridium component,a rhenium component, a tin component, and an alkali or alkaline earthcomponent with a porous carrier material. These components arefurthermore present in amounts sufficient to result in the catalyticcomposite containing, on an elemental basis, about 0.01 to about 2 wt. %platinum or palladium, about 0.01 to about 5 wt. % of the alkali metalor alkaline earth metal, about 0.01 to about 2 wt. % iridium, about 0.01to about 2 wt. % rhenium and about 0.01 to about 5 wt. % tin. Inaddition, substantially all of the platinum or palladium, iridium, andrhenium components are present as the corresponding elemental metals andsubstantially all of the tin component is present in an oxidation stateabove that of the elemental metal.

Another embodiment pertains to a method for dehydrogenating adehydrogenatable hydrocarbon which comprises contacting the hydrocarbonwith the catalytic composite described in the third embodiment atdehydrogenation conditions.

Other objects and embodiments of the present invention involve specificdetails regarding essential and preferred catalytic ingredients,preferred amounts of ingredients, suitable methods of multimettaliccomposite preparation, suitable dehydrogenatable hydrocarbons, operatingconditions for use in the dehydrogenation process, and the likeparticulars. These are hereinafter given in the following detaileddiscussion of each of these facets of the present invention.

Regarding the dehydrogenatable hydrocarbon that is subjected to themethod of the present invention, it can, in general, be an organiccompound having 2 to 30 carbon atoms per molecule and containing atleast 1 pair of adjacent carbon atoms having hydrogen attached thereto.That is, it is intended to include within the scope of the presentinvention, the dehydrogenation of any organic compound capable of beingdehydrogenated to produce products containing the same number of carbonatoms but fewer hydrogen atoms, and capable of being vaporized at thedehydrogenation temperatures used herein. More particularly, suitabledehydrogenatable hydrocarbons are: aliphatic compounds containing 2 to30 carbon atoms per molecule, alkylaromatic hydrocarbons where the alkylgroup contains 2 to 6 carbon atoms, and naphthenes or alkyl-substitutednaphthenes. Specific examples of suitable dehydrogenatable hydrocarbonsare: (1) alkanes such as ethanes, propane, n-butane, isobutane,n-pentane, isopentane, n-hexane, 2-methylhexane, 2-methylpentane,2,2-dimethylbutane, n-heptane, 2-methylhexane, 2,2,3-trimethylbutane,and the like compounds; (2) naphthenes such as cyclopentane,cyclohexane, methylcyclopentane, ethylcyclopentane,n-propylcyclopentane, 1,3-dimethylcyclohexane, and the like compounds;and (3) alkylaromatics such as ethylbenzene, n-butylbenzene,1,3,5-triethylbenzene, isopropylbenzene, isobutylbenzene,ethylnaphthalene, and the like compounds.

In a preferred embodiment, the dehydrogenatable hydrocarbon is a normalparaffin hydrocarbon having about 4 to about 30 carbon atoms permolecule. For example, normal paraffin hydrocarbons containing about 10to 18 carbon atoms per molecule are dehydrogenated by the subject methodto produce the corresponding normal mono-olefin which can, in turn, bealkylated with benzene and sulfonated to make alkylbenzene sulfonatedetergents having superior biodegradibility. Likewise, n-alkanes having10 to 18 carbon atoms per molecule can be dehydrogenated to thecorresponding normal mono-olefin which, in turn, can be sulfonated orsulfated to make excellent detergents. Similarly, n-alkanes having 6 to10 carbon atoms can be dehydrogenated to form the correspondingmono-olefin which can, in turn, be hydrated to produce valuablealcohols. Preferred feed streams for the manufacture of detergentintermediates contain a mixture of 4 or 5 adjacent normal paraffinhomologues such as C₁₀ to C₁₃, C₁₁ to C₁₄, C₁₁ to C₁₅, and the likemixtures.

The multimetallic catalyst of the present invention comprises a porouscarrier material or support having combined therewith catalyticallyeffective amounts of a platinum or palladium component, an iridiumcomponent, a rhenium component, a tin component and in the preferredcase, an alkali or alkaline earth component. Considering first theporous carrier material utilized in the present invention, it ispreferred that the material be a porous, adsorptive, high-surface areasupport having a surface area of about 25 to about 500 m² /g. The porouscarrier material should be relatively refractory to the conditionsutilized in the hydrocarbon conversion process, and it is intended toinclude within the scope of the present invention carrier materialswhich have traditionally been utilized in dual-function hydrocarbonconversion catalysts such as: (1) activated carbon, coke, or charcoal;(2) silica or silica gel, silicon carbide, clays, and silicatesincluding those synthetically prepared and naturally-occurring, whichmay or may not be acid treated, for example, attapulgus clay, chinaclay, diatomaceous earth, fuller's earth, kaoline, kieselguhr, etc.; (3)ceramics, porcelain, crushed firebrick, bauxite; (4) refractoryinorganic oxides such as alumina, titanium dioxide, zirconium dioxide,chromium oxide, zinc oxide, magnesia, thoria, boria, silica-alumina,silica-magnesia, chromiaalumina, alumina-boria, silica-zirconia, etc.;(5) crystalline zeolitic aluminosilicates such as naturally-occurring orsynthetically-prepared mordenite and/or faujasite, either in thehydrogen form or in a form which has been treated with multi-valentcations; (6) spinels such as MgAl₂ O₄, FeAl₂ O₄, ZnAl₂ O₄, MnAl₂ O₄,CaAl₂ O₄ and other like compounds having the formula MO.sup.. Al₂ O₃where M is a metal having a valence of 2; and (7) combinations ofelements from one or more of these groups. The preferred porous carriermaterial for use in the present invention are refractory inorganicoxides, with best results obtained with an alumina carrier material.Suitable alumina materials are the crystalline aluminas known as thegammas-, eta-, and theta-alumina, with gamma- or eta-alumina giving bestresults. In addition, in some embodiments the alumina carrier materialmay contain minor proportions of other well-known refractory inorganicoxides such as silica, zirconia, magnesia, etc.; however, the preferredsupport is substantially pure gamma- or eta-alumina. Preferred carriermaterials have an apparent bulk density of about 0.3 to about 0.7 g/ccand surface area characteristics such that the average pore diameter isabout 20 to 300 Angstroms, the pore volume is about 0.1 to about 1 cc/gand the surface area is about 100 to about 500 m² /g. In general, bestresults are typically obtained with a gamma-alumina carrier materialwhich is used in the form of spherical particles having: a relativelysmall diameter (i.e. typically about 1/16 inch), an apparent bulkdensity of about 0.5 to about 0.6 g/cc, a pore volume of about 0.4 cc/g,and a surface area of about 175 m² /g.

The preferred alumina carrier material may be prepared in any suitablemanner and may be synthetically prepared or natural occurring. Whatevertype of alumina is employed it may be activated prior to use by one ormore treatments including drying, calcination, steaming, etc., and itmay be in a form known as activated alumina, activated alumina ofcommerce, porous alumina, alumina gel, etc. For example, the aluminacarrier may be prepared by adding a suitable alkaline reagent, such asammonium hydroxide to a salt of aluminum such as aluminum chloride,aluminum nitrate, etc., in an amount to form an aluminum hydroxide gelwhich upon drying and calcining is converted to alumina. The aluminacarrier may be formed in any desired shape such as spheres, pills,cakes, extrudates, powders, granules, etc., and utilized in any desiredsize. For the purpose of the present invention a particularly preferredform of alumina is the sphere; and alumina spheres may be continuouslymanufactured by the well-known oil drop method which comprises; formingan alumina hydrosol by any of the techniques taught in the art andpreferably by reacting aluminum metal with hydrochloric acid, combiningthe resulting hydrosol with a suitable gelling agent and dropping theresultant mixture into an oil bath maintained at elevated temperatures.The droplets of the mixture remain in the oil bath until they set andform hydrogel spheres. The spheres are then continuously withdrawn fromthe oil bath and typically subjected to specific aging treatments in oiland an ammoniacal solution to further improve their physicalcharacteristics. The resulting aged and gelled particles are then washedand dried at a relatively low temperature of about 300° F. to about 400°F. and subjected to a calcination procedure at a temperature of about850° F. to about 1300° F. for a period of about 1 to about 20 hours.This treatment effects conversion of the alumina hydrogel to thecorresponding crystalline gamma-alumina. See the teachings of U.S. Pat.No. 2,620,314 for additional details.

One essential constituent of the multimetallic catalyst of the presentinvention is a tin component. It is an essential feature of the presentinvention that the tin component is present in the multimetalliccomposite in an oxidation state above that of the elemental metal. Thatis, the tin component will exist in the present catalytic composite ineither the +2 or +4 oxidation state with the latter being the mostlikely state. Accordingly, the tin component will be present in thecomposite as a chemical compound, such as the oxide, sulfide, halide,etc., wherein the tin moiety is in the required oxidation state, or as achemical combination with the carrier material in which combination thetin moiety exists in this higher oxidation state. On the basis of theevidence currently available, it is believed that the tin component inthe subject composite exists in the form of tin oxide -- that is, asstannic or stannous oxide. It is important to note that this limitationon the state of the tin component requires extreme care in thepreparation and use of the subject composite in order to insure that itis subjected to oxidation conditions effective to produce tin oxide andthat it is not thereafter subjected to high temperature reductionconditions effective to produce the tin metal. Preferably, the tincomponent is used in an amount sufficient to result in the finalcatalytic composite containing, on an elemental basis, about 0.01 toabout 5 wt. % tin, with best results typically obtained with about 0.1to about 2 wt. % tin.

This tin component may be incorporated in the multimetallic catalyticcomposite in any suitable manner known to result in a relatively uniformdistribution of the tin moiety in the carrier material, such as bycoprecipitation or cogellation with the porous carrier material, ionexchange with the carrier material or impregnation of the carriermaterial at any stage in the preparation. It is to be noted that it isintended to include within the scope of the present invention allconventional methods for incorporating a uniform distribution of themetallic component in a catalytic composite, and the particular methodof incorporation used is not deemed to be an essential feature of thepresent invention. One preferred method of incorporating the tincomponent into the catalytic composite involves coprecipitating the tincomponent during the preparation of the preferred refractory oxidecarrier material. In the preferred case, this involves the addition ofsuitable soluble tin compounds such as stannous or stannic halide to thealumina hydrosol, and then combining the hydrosol with a suitablegelling agent, and dropping the resulting mixture into an oil bath,etc., as explained in detail hereinbefore. Following the calcinationstep, there is obtained a carrier material comprising an intimatecombination of alumina and stannic oxide. Another preferred method ofincorporating the tin component into the catalytic composite involvesthe utilization of a soluble, decomposable compound of tin to impregnatethe porous carrier material. Thus, the tin component may be added to thecarrier material by commingling the latter with an aqueous solution of asuitable tin salt or water-soluble compound of tin such as stannousbromide, stannous chloride, stannic chloride, stannic chloridepentahydrate, stannic chloride tetrahydrate, stannic chloridetrihydrate, stannic chloride diamine, stannic trichloride bromide,stannic chromate, stannous fluoride, stannic fluoride, stannic iodide,stannic sulfate, stannic tartrate, and the like compounds. Theutilization of a tin chloride compound, such as stannous or stannicchloride is particularly preferred. In general, the tin component can beimpregnated either prior to, simultaneously with, or after the othermetallic components are added to the carrier material. However, I havefound that excellent results are obtained when the tin component isimpregnated simultaneously with the other metallic components. In fact,a preferred impregnation solution contains chloroplatinic acid,perrhenic acid, chloroiridic acid, stannous or stannic chloride and astrong acid such as hydrochloric acid, nitric acid and the like.

Regardless of which tin compound is used in the preferred impregnationstep, it is extremely important that the tin component be uniformlydistributed throughout the carrier material during this step. In orderto achieve this objective it is necessary to maintain the pH of theimpregnation solution in at a relatively low level, a range of about 1to about 7, preferably 1 to about 3, and to dilute the impregnationsolution to a volume which is approximately equivalent to or greaterthan the volume of the carrier material which is impregnated. It ispreferred to use a volume ratio of impregnation solution to carriermaterial of at least 0.5:1 and preferably about 0.75:1 to about 2:1 ormore. Similarly, it is preferred to use a relatively long contact timeduring the impregnation step ranging from about 1/4 hour up to about 1/2hour or more before drying to remove excess solvent in order to insure ahigh dispersion of the tin component into the carrier material. Thecarrier material, is, likewise, preferably constantly agitated duringthis preferred impregnation step.

A second essential ingredient of the subject multimetallic catalyst isthe platinum or palladium component. That is, it is intended to coverthe use of platinum or palladium or mixtures thereof as a secondcomponent of the present composite. It is an essential feature of thepresent invention that substantially all of this platinum or palladiumcomponent exists within the final catalytic composite in the elementalmetallic state. Generally, the amount of this component present in thefinal catalyst composite is small compared to the quantities of theother components combined therewith. In fact, the platinum or palladiumcomponent generally will comprise about 0.01 to about 2 wt. % of thefinal catalytic composite, calculated on an elemental basis. Excellentresults are obtained when the catalyst contains about 0.05 to about 1wt. % of the platinum or palladium metal.

This platinum or palladium component may be incorporated in thecatalytic composite in any suitable manner known to result in arelatively uniform distribution of this component in the carriermaterial such as coprecipitation or cogellation, ion-exchange, orimpregnation. The preferred method of preparing the catalyst involvesthe utilization of a soluble, decomposable compound of platinum orpalladium to impregnate the carrier material in a relatively uniformmanner. For example, this component may be added to the support bycommingling the latter with an aqueous solution of chloroplatinic orchloropalladic acid. Other water-soluble compounds of platinum orpalladium may be employed in impregnation solutions and include ammoniumchloroplatinate, bromoplatinic acid, platinum dichloride, platinumtetrachloride hydrate, platinum dichlorocarbonyl dichloride,dinitrodiaminoplatinum, palladium chloride, palladium nitrate, palladiumsulfate, etc. The utilization of a platinum or palladium chloridecompound, such as chloroplatinic or chloropalladic acid, is generallypreferred. Hydrogen chloride, nitric acid or the like acid is alsogenerally added to the impregnation solution in order to furtherfacilitate the uniform distribution of the metallic component throughoutthe carrier material. In addition, it is generally preferred toimpregnate the carrier material after it has been calcined in order tominimize the risk of washing away the valuable platinum or palladiumcompounds; however, in some cases it may be advantageous to impregnatethe carrier material when it is in a gelled state.

Yet another essential ingredient of the present multimetallic catalyticcomposite is an iridium component. It is of fundamental importance thatsubstantially all of the iridium component exists within the catalyticcomposite of the present invention in the elemental metallic state andthe subsequently described reduction procedure is designed to accomplishthis objective. The iridium component may be utilized in the compositein any amount which is catalytically effective, with the preferredamount being about 0.01 to about 2 wt. % thereof, calculated on anelemental iridium basis. Typically best results are obtained with about0.05 to about 1 wt. % iridium. It is, additionally, preferred to selectthe specific amount of iridium from within this broad weight range as afunction of the amount of the platinum or palladium component, on anatomic basis, as is explained hereinafter.

This iridium component may be incorporated into the catalytic compositein any suitable manner known to those skilled in the catalystformulation art which results in a relatively uniform dispersion ofiridium in the carrier material. In addition, it may be added at anystage of the preparation of the composite -- either during preparationof the carrier material or thereafter -- and the precise method ofincorporation used is not deemed to be critical. However, best resultsare thought to be obtained when the iridium component is relativelyuniformly distributed throughout the carrier material, and the preferredprocedures are the ones known to result in a composite having thisrelatively uniform distribution. One acceptable procedure forincorporating this component into the composite involves cogelling orcoprecipitating the iridium component during the preparation of thepreferred carrier material, alumina. This procedure usually comprehendsthe addition of a soluble, decomposable compound of iridium such asiridium tetrachloride to the alumina hydrosol before it is gelled. Theresulting mixture is then finished by conventional gelling, aging,drying and calcination steps as explained hereinbefore. A preferred wayof incorporating this component is an impregnation step wherein theporous carrier material is impregnated with a suitableiridium-containing solution either before, during or after the carriermaterial is calcined. Preferred impregnation solutions are aqueoussolutions of water soluble, decomposable iridium compounds such asiridium tribromide, iridium dichloride, iridium tetrachloride, iridiumoxalic acid, iridium sulfate, potassium iridochloride, chloroiridicacid, hexamine iridium chloride, and the like compounds. Best resultsare ordinarily obtained when the impregnation solution is an aqueoussolution of chloroiridic acid or sodium chloroiridate. This componentcan be added to the carrier material, either prior to, simultaneouslywith or after the other metallic components are combined therewith. Bestresults are usually achieved when this component is added simultaneouslywith the other metallic components. In fact, excellent results areobtained with a one step impregnation procedure using an aqueoussolution comprising chloroplatinic or chloropalladic acid, chloroiridicacid, and a strong acid such as hydrochloric acid, nitric acid, etc.

Yet another essential component of the catalyst of the present inventionis the rhenium component. It is an essential feature of the presentinvention that substantially all of the rhenium component of thecatalyst is present therein as the elemental metal, and the hereinafterdescribed reduction step is specifically designed to reduce thiscomponent along with the platinum or palladium component and the iridiumcomponent to the corresponding metallic states. The rhenium component ispreferably utilized in an amount sufficient to result in a finalcatalytic composite containing about 0.01 to about 2 wt. % rhenium andpreferably about 0.05 to about 1, calculated on an elemental basis.

The rhenium component may be incorporated in the catalytic composite inany suitable manner and at any stage in the preparation of the catalyst.It is generally advisable to incorporate the rhenium component in animpregnation step after the porous carrier material has been formed inorder that the expensive metal will not be lost due to washing andpurification treatments which may be applied to the carrier materialduring the course of its production. Although any suitable method forincorporating a catalytic component in a porous carrier material can beutilized to incorporate the rhenium component, the preferred procedureinvolves impregnation of the porous carrier material. The impregnationsolution can, in general, be a solution of a suitable soluble,decomposable rhenium salt such as ammonium perrhenate, sodiumperrhenate, potassium perrhenate, and the like salts. In addition,solutions of rhenium halides such as rhenium chloride may be used; thepreferred impregnation solution is, however, an aqueous solution ofperrhenic acid. The porous carrier material can be impregnated with therhenium component either prior to, simultaneously with, or after theother components mentioned herein are combined therewith. Best resultsare ordinarily achieved when the rhenium component is impregnatedsimultaneously with the platinum or palladium, cin and iridiumcomponents. In fact, excellent results are obtained with a one stepimpregnation procedure utilizing as an impregnation solution, an aqueoussolution of chloroplatinic acid, chloroiridic acid, perrhenic acid,stannic chloride, and a strong acid such as hydrochloric acid, nitricacid and the like.

Regarding the preferred amounts of te various metallic components of thesubject catalyst, I have found it to be a good practice to specify theamounts of the iridium component, the rhenium component, and the tincomponent as a function of the amount of the platinum or palladiumcomponent. On this basis, the amount of the rhenium component isordinarily selected so that the atomic ratio of rhenium to platinum orpalladium metal contained in the composite is about 0.1:1 to about 3:1,with the preferred range being about 0.25:1 to about 1.5:1. Similarly,the amount of the tin component is ordinarily selected to produce acomposite containing an atomic ratio of tin to platinum or palladiummetal of about 0.1:1 to about 3:1, with the preferred range being about0.25:1 to about 2:1. In the same manner, the amount of the iridiumcomponent is preferably selected so that the atomic ratio of iridium toplatinum or palladium is about 0.1:1 to about 2:1.

Another significant parameter of the instant catalyst is the "totalmetals content" which is defined to be the sum of the platinum orpalladium component, the iridium component, the rhenium component, andthe tin component, calculated on an elemental tin, rhenium, iridium andplatinum or palladium metal basis. Good results are ordinarily obtainedwith the subject catalyst when this parameter is fixed at a value ofabout 0.15 to about 5 wt. %, with best results ordinarily achieved at ametals loading of about 0.3 to about 2 wt. %.

Integrating the above discussion of each of the essential components ofthe multimetallic catalytic composite, it is evident that a particularlypreferred catalytic composite comprises a combination of a platinumcomponent, an iridium component, a rhenium component and a tin componentwith an alumina carrier material in amounts sufficient to result in thecomposite containing about 0.05 to about 1 wt. % platinum, about 0.05 toabout 1 wt. % iridium, about 0.05 to about 1 wt. % rhenium, and about0.05 to about 2 wt. % tin. Accordingly, specific examples of especiallypreferred catalytic composites are as follows: (1) a catalytic compositecomprising a combination of 0.5 wt. % tin, 0.5 wt. % rhenium, 0.5 wt. %iridium and 0.75 wt. % platinum with an alumina carrier material; (2) acatalytic composite comprising a combination of 0.1 wt. % tin, 0.1 wt. %rhenium, 0.1 wt. % iridium and 0.1 wt. % platinum with an aluminacarrier material; (3) a catalytic composite comprising a combination ofabout 0.375 wt. % tin, 0.375 wt. % rhenium, 0.375 wt. % platinum and0.375 wt. % iridium with an alumina carrier material; (4) a catalyticcomposite comprising a combination of 0.12 wt. % tin, 0.1 wt. % rhenium,0.2 wt. % platinum and 0.2 wt. % iridium with an alumina carriermaterial; (5) a catalytic composite comprising a combination of 0.25 wt.% tin, 0.25 wt. % platinum, 0.25 wt. % iridium and 0.25 wt. % rheniumwith an alumina carrier material; and, (6) a catalytic compositecomprising a combination of 0.2 wt. % tin, 0.2 wt. % rhenium, 0.2 wt. %platinum and 0.2 wt. % iridium with an alumina carrier material. Theamounts of the components reported in these examples are, of course,calculated on an elemental basis.

As indicated above, a preferred embodiment of the present inventioninvolves use of a catalytic composite containing an alkali or alkalineearth component. More specifically, this component is selected from thegroup consisting of the alkali metals -- cesium, rubidium, potassium,sodium, and lithium -- and of the alkaline earth metals -- calcium,strontium, barium, and magnesium. This component may exist within thecatalytic composite as a relatively stable compound such as the oxide orsulfide or in combination with one or more of the other components ofthe composite, or in combination with an alumina carrier material suchas in the form of a metal aluminate. Since, as is explained hereinafter,the composite containing the alkali or alkaline earth is always calcinedor oxidized in an air atmosphere before use in the conversion ofhydrocarbons, the most likely state this component exists in during usein dehydrogenation is in the form of the corresponding metallic oxide.Regardless of what precise form in which it exists in the composite, theamount of this component utilized is preferably selected to provide acomposite containing about 0.01 to about 5 wt. % of the alkali oralkaline earth metal, and more preferably, about 0.05 to about 2.5 wt.%. Best results are ordinarily achieved when this component is acompound of lithium or potassium and particularly lithium oxide orpotassium oxide.

This alkali or alkaline earth component may be combined with the porouscarrier material in any manner known to those skilled in the art such asby impregnation, coprecipitation, physical admixture, ion exchange, etc.However, the preferred procedure involves impregnation of the carriermaterial either before or after it is calcined and either before, duringor after the other components are added to the carrier material. Bestresults are ordinarily obtained when this component is added after theplatinum or palladium, iridium, rhenium and tin components because itserves to neutralize the acid used in the preferred impregnationprocedure for incorporation of these components. In fact, it ispreferred to add the previously specified metallic components, dry andoxidize the resulting composite, then treat the oxidized composite withsteam in order to remove residual acidity, and then add this componentby means of an impregnation procedure. Typically, the impregnation ofthe oxidized composite or of the carrier material is performed bycontacting same with a solution of a suitable decomposable compound orsalt of the desired alkali or alkaline earth metal. Hence, suitablecompounds include the halides, sulfates, nitrates, acetates, carbonates,phosphates, and the like compounds. For example, excellent results areobtained by impregnating the carrier material, after the platinum orpalladium, iridium, rhenium and tin components have been combinedtherewith, with an aqueous solution of lithium nitrate or potassiumnitrate. Following the incorporation of this component, the resultingcomposite is preferably dried and oxidized in an air atmosphere asexplained hereinafter.

Regardless of the details of how the components of the catalyst arecombined with the porous carrier material, the resulting composite,after one or more of the components are added thereto, generally will bedried at a temperature of about 200° F. to about 600° F. for a period ofabout 2 to 24 hours or more and finally calcined or oxidized at atemperature of about 600° F. to about 1100° F. in an air atmosphere fora period of about 0.5 to about 10 hours, preferably about 1 to about 5hours in order to convert substantially all of the metallic componentsto the corresponding oxide forms. When acidic components are present inany of the reagents used to effect incorporation of any one of thecomponents of the subject composite, it is a good practice to subjectthe resulting composite to a high temperature treatment with steam,either after or before the calcination step described above, in order toremove as much as possible of the undesired acidic component. Forexample, when the platinum or palladium component is incorporated byimpregnating the carrier material with chloroplatinic acid, it ispreferred to subject the resulting composite to a high temperaturetreatment with steam in order to remove as much as possible of theundesired chloride.

It is essential to subject the resultant oxidized multimetalliccatalytic composite to a reduction step with substantially water-freehydrogen prior to its use in the conversion of hydrocarbons. This stepis designed to insure a uniform and finely divided dispersion of themetallic components throughout the carrier material and to selectivelyreduce the platinum or palladium, iridium and rhenium components to thecorresponding elemental metallic states, while maintaining the tincomponent in a positive oxidation state. Preferably, a stream ofsubstantially pure and dry hydrogen (i.e., less than 20 vol. ppm. H₂ O)is used as the reducing agent in this step. The reducing agent iscontacted with the calcined or oxidized composite at reductionconditions, including a temperature of about 800° F. to about 1200° F.,a gas hourly space velocity of about 100 to about 10,000 hr.⁻ ¹ and fora period of time of about 0.5 to 10 hours or more, effective to reducesubstantially all of the platinum or palladium, iridium and rheniumcomponents to the elemental metallic state while maintainingsubstantially all of the tin component in a positive oxidation state.This reduction treatment may be performed in situ as part of a start-upsequence if precautions are taken to predry the plant to a substantiallywater-free state and if a substantially water-free hydrogen stream isused.

The resulting selectively reduced catalytic composite may, in somecases, be beneficially subjected to a presulfiding operation designed toincorporate in the catalytic composite from about 0.05 to about 0.5 wt.% sulfur, calculated on an elemental basis. Preferably, thispresulfiding treatment takes place in the presence of hydrogen and asuitable sulfur-containing compound such as hydrogen sulfide, lowermolecular weight mercaptans, organic sulfides, etc. Typically, thisprocedure comprises treating the selectively reduced catalyst with asulfiding gas such as a mixture containing a mole ratio of H₂ to H₂ S ofabout 10:1 at conditions sufficient to effect the desired incorporationof sulfur, generally including a temperature ranging from about 50° F.up to about 1100° F. or more. This presulfiding step can be performed insitu or ex situ.

According to the method of the present invention, the dehydrogenatablehydrocarbon is contacted with the multimetallic catalytic compositedescribed above in a dehydrogenation zone maintained at dhydrogenationconditions. This contacting may be accomplished by using the catalyst ina fixed bed system, a moving bed system, a fluidized bed system, or in abatch type operation; however, in view of the danger of attrition lossesof the valuable catalyst and of well known operational advantages, it ispreferred to use a fixed bed system. In this system, the hydrocarbonfeed stream is preheated by any suitable heating means to the desiredreaction temperature and then passed into a dehydrogenation zonecontaining a fixed bed of the catalyst previously characterized. It is,of course, understood that the dehydrogenation zone may be one or moreseparate reactors with suitable heating means therebetween to insurethat the desired conversion temperature is maintained at the entrance toeach reactor. It is also to be noted that the reactants may be contactedwith the catalyst bed in either upward, downward, or radial flow fashionwith the latter being preferred. In addition, it is to be noted that thereactants may be in the liquid phase, a mixed liquid-vapor phase, or avapor phase when they contact the catalyst, with best results obtainedin the vapor phase.

Although hydrogen is the preferred diluent for use in the subjectdehydrogenation method, in some cases other art-recognized diluents maybe advantageously utilized such as steam, methane, carbon dioxide, andthe like diluents. Hydrogen is preferred because it serves thedual-function of not only lowering the partial pressure of thedehydrogenatable hydrocarbon, but also suppressing the formation ofhydrogen-deficient, carbonaceous deposits on the catalytic composite.Ordinarily, hydrogen is utilized in amounts sufficient to insure ahydrogen to hydrocarbon mole ratio of about 1:1 to about 20:1, with bestresults obtained in the range of about 1.5:1 to about 10:1. The hydrogenstream charged to the dehydrogenation zone will typically be recyclehydrogen obtained from the effluent stream from this zone after asuitable hydrogen separation step. When utilizing hydrogen in theinstant process, improved results are obtained if water or awater-producing substance (such as an alcohol), ketone, or the likeoxygen-containing decomposable organic compound) is added to thedehydrogenation zone in an amount calculated on the basis of equivalentwater, corresponding to about 100 to about 4,000 wt. ppm. of thehydrocarbon charge stock, with about 1500 to 2500 wt. ppm. of watergiving best results.

Regarding the conditions utilized in the process of the presentinvention, these are generally selected from the dehydrogenationconditions well known to those skilled in the art for the particulardehydrogenatable hydrocarbon which is charged to the process. Morespecifically, suitable conversion temperatures are selected from therange of about 700° to about 1250° F. with a value being selected fromthe lower portion of this range for the more easily dehydrogenatedhydrocarbons such as the long chain normal paraffins and from the higherportion of this range for the more difficultly dehydrogenatedhydrocarbons such as propane, butane, and the like hydrocarbons. Forexample, for the dehydrogenation of C₆ to C₃₀ normal paraffins, bestresults are ordinarily obtained at a temperature of about 800° to about950° F. The pressure utilized is ordinarily selected at a value which isas low as possible consistent with the maintenance of catalyst stabilityand is usually about 0.1 to about 10 atmospheres with best resultsordinarily obtained in the range of about 0.5 to about 3 atmospheres. Inaddition, a liquid hourly space velocity (calculated on the basis of thevolume amount, as a liquid, of hydrocarbon charged to thedehydrogenation zone per hour divided by the volume of the catalyst bedutilized) is selected from the range of about 1 to about 40 hr..sup.⁻¹,with best results for the dehydrogenation of long chain normal paraffinstypically obtained at a relatively high space velocity of about 25 to 35hr..sup.⁻¹.

Regardless of the details concerning the operation of thedehydrogenation step, an effluent stream will be withdrawn therefrom.This effluent will usually contain unconverted dehydrogenatablehydrocarbons, hydrogen, and products of the dehydrogenation reaction.This stream is typically cooled and passed to a hydrogen-separating zonewherein a hydrogen-rich vapor phase is allowed to separate from ahydrocarbon-rich liquid phase. In general, it is usually desired torecover the unreacted dehydrogenatable hydrocarbon from thishydrocarbon-rich liquid phase in order to make the dehydrogenationprocess economically attractive. This recovery operation can beaccomplished in any suitable manner known to the art such as by passingthe hydrocarbon-rich liquid phase through a bed of suitable adsorbentmaterial which has the capability to selectively retain thedehydrogenated hydrocarbons contained therein or by contacting same witha solvent having a high selectivity for the dehydrogenated hydrocarbon,or by a suitable fractionation scheme where feasible. In the case wherethe dehydrogenated hydrocarbon is a mono-olefin, suitable adsorbentshaving this capability are activated silica gel, activated carbon,activated alumina, various types of specially prepared molecular sieves,and the like adsorbents. In another typical case, the dehydrogenatedhydrocarbons can be separated from the unconverted dehydrogenatablehydrocarbons by utilizing the inherent capability of the dehydrogenatedhydrocarbons to easily enter into several well known chemical reactionssuch as alkylation, oligomerization, halogenation, sulfonation,hydration, oxidation, and the like reactions. Irrespective of how thedehydrogenated hydrocarbons are separated from the unreactedhydrocarbons, a stream containing the unreacted dehydrogenatablehydrocarbons will typically be recovered from this hydrocarbonseparation step and recycled to the dehydrogenation step. Likewise, thehydrogen phase present in the hydrogen-separating zone will be withdrawntherefrom, a portion of it vented from the system in order to remove thenet hydrogen make, and the remaining portion is typically recycledthrough suitable compressing means to the dehydrogenation step in orderto provide diluent hydrogen therefor.

In a preferred embodiment of the present invention wherein long chainnormal paraffin hydrocarbons are dehydrogenated to the correspondingnormal mono-olefins, a preferred mode of operation of this hydrocarbonrecovery step involves an alkylation reaction. In this mode, thehydrocarbon-rich liquid phase withdrawn from the hydrogen-separatingzone is combined with a stream containing an alkylatable aromatic andthe resulting mixture passed to an alkylation zone containing a suitablehighly acid catalyst such as an anhydrous solution of hydrogen fluoride.In the alkylation zone the mono-olefins react with alkylatable aromaticwhile the unconverted normal paraffins remain substantially unchanged.The effluent stream from the alkylation zone can then be easilyseparated, typically by means of a suitable fractionation system, toallow recovery of the unreacted normal paraffins. The resulting streamof unconverted normal paraffins is then usually recycled to thedehydrogenation step of the present invention.

The following working examples are introduced to illustrate further thenovelty, mode of operation, utility, and benefits associated with thedehydrogenation method of the present invention. These Examples areintended to be illustrative rather than restrictive.

These Examples are all performed in a laboratory scale dehydrogenationplant comprising a reactor, a hydrogen separating zone, a heating means,cooling means, pumping means, compressing means, and the like equipment.In this plant, the feed stream containing the dehydrogenatablehydrocarbon is combined with a hydrogen stream and the resultant mixtureheated to the desired conversion temperature, which refers herein to thetemperature maintained at the inlet to the reactor. The heated mixtureis then passed into contact with the catalyst which is maintained as afixed bed of catalyst particles in the reactor. The pressures reportedherein are recorded at the outlet from the reactor. An effluent streamis withdrawn from the reactor, cooled, and passed into thehydrogen-separating zone wherein a hydrogen gas phase separates from ahydrocarbon-rich liquid phase containing dehydrogenated hydrocarbons,unconverted dehydrogenatable hydrocarbons, and a minor amount of sideproducts of the dehydrogenation reaction. A portion of the hydrogen-richgas phase is recovered as excess recycle gas with the remaining portionbeing continuously recycled through suitable compressive means to theheating zone as described above. The hydrocarbon-rich liquid phase fromthe separating zone is withdrawn therefrom and subjected to analysis todetermine conversion and selectivity for the desired dehydrogenatedhydrocarbon as will be indicated in the Examples. Conversion numbers ofthe dehydrogenatable hydrocarbon reported herein are all calculated onthe basis of disappearance of the dehydrogenatable hydrocarbon and areexpressed in mole percent. Similarly, selectivity numbers are reportedon the basis of moles of desired hydrocarbon produced per 100 moles ofdehydrogenatable hydrocarbon converted.

All of the catalysts utilized in these Examples are prepared accordingto the following general method with suitable modification instoichiometry to achieve the compositions reported in each Example.First, an alumina carrier material comprising 1/16 inch spheres isprepared by: forming an alumina hydroxyl chloride sol by dissolvingsubstantially pure aluminum pellets in a hydrochloric acid solution,adding hexamethylenetetramine to the sol, gelling the resulting solutionby dropping it into an oil bath to form spherical particles of analumina hydrogel, aging and washing the resulting particles with anammoniacal solution and finally drying, calcining, and steaming the agedand washed particles to form spherical particles of gamma-aluminacontaining substantially less than 0.1 wt. % combined chloride.Additional details as to this method of preparing this alumina carriermaterial are given in the teachings of U.S. Pat. No. 2,620,314. Theresulting gamma-alumina particles are then contacted with an aqueousimpregnation solution containing chloroplatinic acid, perrhenic acid,hydrogen chloride, stannous chloride and chloroiridic acid in amountssufficient to yield a final multimetallic catalytic composite containingthe desired amounts of platinum, iridium, rhenium and tin. Thehydrochloric acid is utilized in an amount of about 10 wt. % of thealumina particles. The impregnated spheres are then dried at atemperature of about 225° F. for about an hour and thereafter calcinedor oxidized in an air atmosphere at a temperature of about 500° F. toabout 1000° F. for about 2 to 10 hours effective to convert all of themetallic components to the corresponding oxide forms. In general, it isa good practice to thereafter treat the resulting oxidized particleswith an air stream containing about 10 to about 30% steam at atemperature of about 1000° F. for an additional period of about 5 hoursin order to reduce the residual combined chloride contained in thecatalyst to a value of less than 0.5 wt. % and preferably less than 0.2wt. %. In the cases shown in the Examples where the catalyst utilizedcontains an alkali component, this component is added to the oxidizedand steam-treated multimetallic catalyst in a separate impregnationstep. This second impregnation step involves contacting the oxidizedmultimetallic catalyst with an aqueous solution of a suitabledecomposable salt of the alkali component. For the catalyst utilized inthe present Examples, the salt is either lithium nitrate or potassiumnitrate. The amount of the salt of the alkali metal utilized is chosento result in a final catalyst of the desired composition. The resultingalkali impregnated particles are then dried and calcined in an airatmosphere in much the same manner as is described above following thefirst impregnation step.

In all of the Examples the catalyst is reduced during startup bycontacting with dry hydrogen at conditions including a temperature ofabout 1050° F. for 1 hour at a gas hourly space velocity of about 500hr..sup. ⁻¹, effective to reduce the platinum, iridium and rheniumcomponents to the corresponding elemental metals while maintaining thetin component in a positive oxidation state.

EXAMPLE I

The reactor is loaded with 100 cc's of a catalyst containing, on anelemental basis, 0.75 wt. % platinum, 0.5 wt. % rhenium, 0.5 wt. %iridium, 0.5 wt. % tin and less than 0.15 wt. % chloride. The feedstream utilized is commercial grade isobutane containing 99.7 wt. %isobutane and 0.3 wt. % normal butane. The feed stream is contacted withthe catalyst at a temperature of 1065° F., a pressure of 10 psig., aliquid hourly space velocity of 4.0 hr.⁻ ¹, and a hydrogen tohydrocarbon mole ratio of 2:1. The dehydrogenation plant is lined-out atthese conditions and a 20 hour test period commenced. The hydrocarbonproduct stream from the plant is continuously analyzed by GLC (gasliquid chromotography) and a high conversion of isobutane is observedwith a high selectivity for isobutylene.

EXAMPLE II

The catalyst contains, on an elemental basis, 0.375 wt. % platinum,0.375 wt. % iridium, 0.375 wt. % rhenium, 0.375 wt. % tin, 0.6 wt. %lithium, and 0.15 wt. % combined chloride. The feed stream is commercialgrade normal dodecane. The dehydrogenation reactor is operated at atemperature of 870° F., a pressure of 10 psig., a liquid hourly spacevelocity of 32 hr.⁻ ¹, and a hydrogen to hydrocarbon mole ratio of 8:1.After a line-out period, a 20 hour test period is performed during whichthe average conversion of the normal dodecane is maintained at a highlevel with a selectivity for normal dodecene of about 90%.

EXAMPLE III

The catalyst is the same as utilized in Example II. The feed stream isnormal tetradecane. The conditions utilized are a temperature of 840°F., a pressure of 20 psig., a liquid hourly space velocity of 32hr..sup.⁻¹, and a hydrogen to hydrocarbon mole ratio of 8:1. After aline-out period, a 20 hour test shows an average conversion of about12%, and a selectivity for normal tetradecene of about 90%.

EXAMPLE IV

The catalyst contains, on an elemental basis, 0.375 wt. % platinum, 0.2wt. % rhenium, 0.375 wt. % iridium, 0.25 wt. % tin and 0.6 wt. %lithium, with combined chloride being less than 0.2 wt. %. The feedstream is substantially pure normal butane. The conditions utilized area temperature of 950° F., a pressure of 15 psig., a liquid hourly spacevelocity of 4.0 hr..sup.⁻¹ and a hydrogen to hydrocarbon mole ratio of4:1. After a line-out period, a 20 hour test is performed with anaverage conversion of the normal butane being about 30% and theselectivity for normal butene is about 80%.

EXAMPLE V

The catalyst contains, on an elemental basis. 0.1 wt. % platinum, 0.1wt. % iridium, 0.2 wt. % rhenium, 0.25 wt. % tin, 1.5 wt. % potassium,and less than 0.2 wt. % combined chloride. The feed stream is commercialgrade ethylbenzene. The conditions utilized are a pressure of 15 psig.,a liquid hourly space velocity of 32 hr..sup. ⁻¹. a temperture of 1050°F., and a hydrogen to hydrocarbon mole ratio of 8:1. During a 20 hourtest period, 85% or more of equilibrium conversion of the ethylbenzeneis observed. The selectivity for styrene is about 95%.

It is intended to cover by the following claims, all changes andmodifications of the above disclosure of the present invention whichwould be self-evident to a man of ordinary skill in thecatalyst-formation art or in the hydrocarbon dehydrogenation art.

I claim as my invention:
 1. A method for dehydrogenating adehydrogenatable hydrocarbon comprising contacting said hydrocarbon, atdehydrogenation conditions, with a catalytic composite comprising acombination of a platinum or palladium component, an iridium component,a rhenium component and a tin component with a porous carrier materialin amounts sufficient to result in a composite containing, on anelemental basis, about 0.01 to about 2 wt. % platinum or palladium,about 0.01 to about 2 wt. % iridium, about 0.01 to about 2 wt. %rhenium, and about 0.01 to about 5 wt. % tin, wherein substantially allof the platinum or palladium component, the iridium component and therhenium component are present in the corresponding elemental metallicstate and wherein substantially all of the tin component is present inan oxidation state above that of the elemental metal.
 2. A method asdefined in claim 1 wherein the dehydrogenatable hydrocarbon is admixedwith hydrogen when it contacts the catalytic composite.
 3. A method asdefined in claim 1 wherein the platinum or palladium component isplatinum metal.
 4. A method as defined in claim 1 wherein the tincomponent is tin oxide.
 5. A method as defined in claim 1 wherein theporous carrier material is a refractory inorganic oxide.
 6. A method asdefined in claim 5 wherein the refractory inorganic oxide is gamma- oreta-alumina.
 7. A method as defined in claim 1 wherein thedehydrogenatable hydrocarbon is an aliphatic compound containing 2 to 30carbon atoms per molecule.
 8. A method as defined in claim 1 wherein thedehydrogenatable hydrocarbon is a normal paraffin hydrocarbon containing4 to 30 carbon atoms per molecule.
 9. A method as defined in claim 1wherein the dehydrogenatable hydrocarbon is a naphthene.
 10. A method asdefined in claim 2 wherein the dehydrogenation conditions include atemperature of 700° to 1250° F., a pressure of 0.1 to 10 atmospheres, anLHSV of 1 to 40 and a hydrogen to hydrocarbon mole ratio of about 1:1 toabout 20:1.
 11. A method as defined in claim 1 wherein the compositecontains, on an elemental basis, about 0.05 to about 1 wt. % platinum orpalladium metal, about 0.05 to about 1 wt. % iridium, about 0.05 toabout 1 wt. % rhenium, and about 0.05 to about 2 wt. % tin.
 12. A methodas defined in claim 1 wherein the metals content of the catalyticcomposite is adjusted so that the atomic ratio of tin to platinum orpalladium is about 0.1:1 to about 3:1, the atomic ratio of rhenium toplatinum or palladium is about 0.1:1 to about 3:1 and the atomic ratioof iridium to platinum or palladium is about 0.1:1 to about 2:1.